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Safety First -- Tech Tip Highlight

Don't press your luck!

Sure, you know how to work on old trucks. Or maybe you're just starting in the hobby. Either way, safety is best learned through OPM (Other Peoples' Mistakes), not OJT!

Either as newly discovered wisdom, or a refresher, please read this article and live safely with your old truck!


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#1403338 Sat Mar 27 2021 11:26 PM
Joined: Feb 2018
Posts: 96
Hello all. Continuing to upgrade my 49 chevy 1/2 ton. I have original style huck brakes on the front of the truck and late model drums on the back. I have seen a disc brake conversion at some parts vendors (Brothers Trucks and Classic Parts) that looks pretty simple. My question is this: can I just do the disc brake conversion upgrade on the front now and use the stock master cylinder with one line coming out and going front and back? I don't really want to tackle changing out the master cylinder and running new brake lines right now. I just want to improve my stopping power. Not happy with the huck style brakes on the front. I've attached a photo of the disc brake conversion I'm looking at.


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Last edited by Darrell Day; Sat Mar 27 2021 11:27 PM.
Joined: Oct 2005
Posts: 3,828
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GM Metric calipers use much more fluid to operate than the old slave cylinders. It would probably be best to upgrade the master, also.

Joined: Feb 2018
Posts: 96
Thanks Mark. After doing some more reading and research, looks like a new dual master cylinder will be in the works. Anyone else tackled this project?

Joined: Jun 2011
Posts: 4,836
‘80’s Chevys used non-power master disc/disc that might work for you, disc brakes need more power or smaller ID masters to make up the power.


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Joined: Nov 2020
Posts: 85
I installed the power disc kit from cpp on my 51 3100. Lines were not hard to manage. Followed the single line to the passenger frame rail and eliminated the T in the line. Ran a line from new master to front and rear and connected respectively where the T was. Had to cut a new hole in the floor to access new master location. Overall, it was one of the best things I’ve done to my truck. It will stop on a dime and I got tapered roller front wheel bearings to boot.

Joined: Feb 2019
Posts: 3,194
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Originally Posted by Sludgeburner
I installed the power disc kit from cpp on my 51 3100..
Is you truck a manual transmission? Most of the kits I see for power assist master cylinders state the they are for an automatic tranny. If yours is a manual, how and where did install the master. Did you modify the rear crossmember?

Last edited by Phak1; Sun Mar 28 2021 12:46 PM.

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I did the brake upgrade on 1950 1/2t GMC. Mine was the CPP complete kit.

Disk brakes require higher brake pressure to the disks. So you absolutely need a new master and proportioning valve that supplies high brake pressure to the front and reduced or metered pressure to the rear drums.

If your doing this once the power brakes master is the way to go to get full benefit.

Most of the brake kits are very similar some actually are the same kit sold by supplier and dropped shipped for various vendors. There are variations in some kits.

I did the front hubs and bearing upgrade at the same time.

The clearance for the manual transmission seems to be a moving target. Multiple reports the kit just bolts I. With no conflicts.
My rear transmission cross member was missing. Many are missing and there are multiple prior posts on the crossmember topic.

I used my restored truck with out the cross member with the drum brakes, upgraded front disks without crossmember with no issues, then added rear transmission crossmember ( aftermarket ) (on a whim) could detect no difference in the brakes or driveline function.

My brake lines and master were replaced during the restoration. The front and rear lines were separated near the master during the upgrade to allow for the dual master.

I too ........believe the disk upgrade with dual master is one of best mods, right there with seat belts.

Last edited by showkey; Sun Mar 28 2021 10:50 PM.
Joined: Sep 2007
Posts: 436
I've been thinking about doing this for many years. I'd like to keep the 4 speed. Some sources have stated that a 1" bore Corvette master cylinder from 1967 to 1976 will work if going with no power. An aftermarket crossmember came with the truck so that is an option as showkey has stated. I found that updating to a dual master cyclinder was a relatively easy project. I used a cyclinder from a 60's something GM. It was from the first year GM used a dual master cylinder. Works well with the original huck brakes.

It's a small world, but I wouldn't want to paint it.

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